1. Field of the Invention
This invention relates to the measurement and display of the altitude, longitude and latitude (hereinafter xe2x80x9c3Dxe2x80x9d) position of aircraft at any time while in flight, on the ground, during take-off or during landing within gate-to-gate.
2. Description of the Prior Art
At present, the 3D position of aircraft is determined onboard the aircraft using GPS or Inertial Navigation System (INS) with altimeters or OMEGA (LORAN) with altimeters or VOR (radial position to known ground station position) (TACAN)/DME (distance measuring equipment) with altimeters. INS is independent of the ground systems measuring the movement of the aircraft in flight and is used in conjunction with DME to measure the aircraft distance to certain ground positions. The 3D position of an aircraft is also determined by ground stations using primary 3D radars (which use reflective signals to provide a conventional xe2x80x9creturnxe2x80x9d signal or xe2x80x9cblipxe2x80x9d on a radar screen) which provide 2D position (These radars do not use transponders and do not provide altitude.) and by secondary radars (MSSR) which utilize an aircraft identification code and the altitude received from the in flight aircraft transponder. The problem with the aircraft and ground based systems is that they are not synchronized and therefore may not manifest the same data. The 3D position determined by the aircraft in flight is determined by different equipment than the 3D position determined by a ground station. The aircraft in flight determined position therefore is not the same as the position as determined by the ground station(s). If the aircraft pilot desires to know the 3D position of his aircraft as determined by the ground station, the ground station must communicate this via a communication channel on request of the aircraft. More importantly, each aircraft in flight or on the ground has no direct information about any other aircraft in its vicinity. This information may be obtained in present day systems only by communication between pilots and the ground stations. Collision avoidance systems do not provide the 3D position of other aircraft, but only provide a warning to the pilot of a given aircraft to take some evasive action to avoid another aircraft in its vicinity.
GPS positioning, while more accurate than a ground positioning system, is not used as a primary system on in-flight aircraft since it is not considered reliable as a primary positioning system due to many factors. Such factors include weakness of the signals (the satellites are 11,000 miles from earth), interference by atmospheric conditions, and the fact that the GPS receiver could be jammed intentionally or unintentionally at any time. GPS is not approved as a primary system for determining aircraft position.
In a still further aspect, a minimum of four ground stations including a ground master station is included with the remaining stations forming slave stations, each station and aircraft having a unique ID code, each station and aircraft including transmitter/receiver means for communicating with each other a plurality of information signals, each signal from a ground station including the ground station ID code and each aircraft signal including an aircraft ID code, said calculating means for calculating the distances based on the transmission delays of said information signals to and from the aircraft and ground stations, a portion of said signals including said calculated distances.
The main disadvantage of the existing ATC system is due to its internal infrastructure which can not be integrated in a unique virtual system in aircraft and on the ground due to the use of too many systems based on different technologies. These technologies, due to their differences, perform the calculation of the aircraft""s 3D position, using an excessively large frequency spectrum and leave little frequency spectrum space for voice/data communication channels between aircraft and between aircraft and air traffic control centers. This is considered by the present inventor to constitute a significant disadvantage of the present systems among others. The present inventor recognizes a demand by travelers onboard aircraft for use of frequency spectrum for business and personal purposes. Such spectrum is presently not available due to the primary use of the different present 3D positioning technologies which take up the available frequency spectrum.
A reliable GPS positioning determining system with INS and appropriate communication means between aircraft and between aircraft and ATC centers could replace all other systems and leave enough frequency spectrums for today and future communication needs.
In order to obtain a reliable GPS that could be approved as primary navigation system onboard of each aircraft, the US FAA developed a WAAS/LAAS concept using satellites which should cover the needs of future integrated Air Traffic Management (ATM) System as defined by the AIR TRAFFIC STRATEGY FOR 2000+document, adopted by ICAO published by Eurocontrol, November 1998. Such a system would use a low orbit satellite system in conjunction with a local airport station (LAAS), local augmented Area Satellite forming a new primary system. Until such concept will prove its performances and which is subject to development into real world hardware, the need exists for determining simultaneously and independently of each other, the synchronized and precise 3D position of each aircraft onboard each aircraft and the same 3D position of all aircraft in the airspace dedicated to an ATC center, to be determined by each aircraft and by that ATC system. Without such performances, any future ATM system (air traffic management system) can not comprise a truly integrated synchronized system. Consequently, the ATM system capacity is still limited and will generate delays and high costs for operation.
Present air traffic control systems utilize flight planning and preassigned routes. This limits the amount of air traffic in a given space and is also wasteful because it is not based on the shortest route between departure and arrival destinations, but on the availability of the prearranged air routes or xe2x80x9chighways.xe2x80x9d It is recognized in the AIR TRAFFIC STRATEGY FOR 2000+document that freer flight paths not restricted to prearranged routes will increase the availability of space for additional aircraft. But implementation of such concepts awaits future development of the necessary technologies. There is an urgent need for solutions to the present air traffic control systems which is saturated and at its limit for air traffic capacity. To increase capacity, steps are being taken to decrease aircraft spacing, for example, during take off and landing and in holding patterns. This is not a viable long tern solution to the problem of a need to more efficiently utilized the available space and frequency spectrum allotted to air traffic control.
A need is recognized by the present inventor for a system which can compute onboard each aircraft its actual 3D position and simultaneously and independently of any other 3D computing system, compute the 3D position of each aircraft in conjunction with the appropriate Air Traffic Control (ATC) center responsible for that airspace which may be for a given airport, an Area Control Center (ACC), e.g., a 300 mile radius, which controls the area and airspace about the airport, an Approach Area (APP), i.e., the runway(s) area or an airport tower (TWR) which controls the local air space at the airport. The same need is applicable to any area where overall mobile ground station positions are controlled.
The aforementioned needs are provided according to the present invention which provides a precise 3D position calculation onboard of each aircraft and simultaneously and independently of the aircraft calculation, provides the same synchronized 3D position calculation on the ground at each ATC center location.
A surveillance system for air traffic control in selected ATC areas according to the present invention comprises first means for independently and simultaneously determining the 3D location in flight and on the ground of all active aircraft in the selected aircraft ATC area; and second means onboard each aircraft for indicating the determined 3D locations of all said active aircraft.
In one aspect, the first means comprises a plurality of ground stations corresponding to each said selected area, each said ground station including a first surveillance module for determining the 3D position of all associated aircraft in said selected area.
In a further aspect, the first surveillance modules in each of the ground stations are identical and further including a second surveillance module in each of the aircraft identical to the ground station modules, each first and second modules including calculating means for calculating the 3D position of all said aircraft based on the measured distance between each aircraft and each ground station.
In a further aspect, the first and second surveillance modules each include 3D position calculating means for calculating the distance between each aircraft and each ground station.
In a further aspect, means are included for synchronizing each calculating means of each module with each other.
In a still further aspect, a minimum of four ground stations including a ground master station is included with the remaining stations forming slave stations, each station and aircraft having a unique code, each station and aircraft including transmitter/receiver means for communicating with each other a plurality of information signals, each signal from a ground station including the ground station ID code and each aircraft signal including an aircraft ID code, said calculating means for calculating the distances based on the transmission delays of said information signals to and from the aircraft and ground stations, a portion of said signals including said calculated distances.
In a further aspect, the first means comprises a plurality of ground stations corresponding to each selected area, each ground station including a first surveillance module for determining the 3D position of all associated aircraft in the selected area.
In a further aspect, the surveillance modules in the ground stations are identical and further including second identical surveillance modules in all of the aircraft, each first and second modules for calculating the 3D position of the associated aircraft for each the second modules.
In a further aspect, the first and second surveillance modules each include 3D position calculating means and a clock and means for synchronizing each calculating means of each module with the clock signal of each other.
In a still further aspect, a system and method is provided for determining, substantially simultaneously and independently of each other, onboard aircraft and on the ground, a synchronized 3D position of all aircraft in an air traffic control area from gate-to-gate.
In a further aspect, the system comprises a plurality of identical ground radio-communication and 3D position determining stations located in each air traffic control area forming a group of ground stations, each group being assigned an ATC area such as ACC, APP and TWR area and for each runway within a TWR area.
In a further aspect, the above arrangement of stations may be provided to any area such as a town, a port or other predefined region.
In a further aspect, each group of ground stations operates at the same frequency and range. For each group, one station is a master and all other ground stations associated with the master station are slave stations. Each ground station includes a GPS receiver and a surveillance module.
In a further aspect, a surveillance module is provided each aircraft and ground station and comprises microproccessor means and dedicated precise oscillator means using DDS-Driven PLL (phase lock loop). In each ground station, a GPS receiver is included with the surveillance module and monitors and validates the ground station calculated 3D position and delivers an accurate reference UTC clock for a period as long as the 3D position provided by GPS is identical with the known geographical coordinates of that ground station (within accuracy of +/xe2x88x9210 meters and clock accuracy within 20 ns (rms) to the UTC.
In a further aspect, the location of all ground stations and their geographical 3D coordinates, assigned unique ID codes, frequency of operation, range and distances between each other are known and are provided to the aircraft operators by a worldwide navigation database.
According to a further aspect, to compute the aircraft 3D position, the aircraft onboard system measures the distance value between the aircraft and all ground stations with their known 3D geographical coordinates. At the same time, the onboard system utilizes the same distance values measured by the ground stations and provided by an ID coded signal thereto from each ground station, between each ground station and the aircraft and such signals are transmitted to the aircraft for determining the aircraft 3D position. The on ground ATC 3D determining system for each ground station in a group of stations associated with a master station includes means for computing independently of each other the 3D position of each aircraft associated with that group of ground stations based on distance values, measured on the ground, between each ground station of the group of ground stations and each aircraft and the known geographical 3D coordinates of the ground stations of the given group of ground stations. group of ground station and aircraft and the known geographical 3D coordinates of the ground stations of the given group of ground stations.
In a further aspect, each master ground station surveillance module generates a surveillance cycle signal and includes means responsive to the surveillance cycle signal for computing an aircraft 3D position for each aircraft, displaying that computed 3D position and for repeating the generation of such cycle signals computation of 3D positions for each aircraft in the airspace allocated to a given ATC center.
In a further aspect, means are provided wherein the master station of each group of stations selects, one by one, at the beginning of a surveillance cycle, each aircraft in the ATC area associated with that master station and group of stations for computing the 3D position of that selected aircraft. Means are included in each master station to receive the ID code of each aircraft in the associated airspace provided by an ATM database.
In a further aspect, a surveillance cycle comprises a plurality of signals generated by the master ground station and contains a defined number of steps wherein a dedicated radio communication signal is transmitted by the master station to a selected receiver and that selected receiver then transmits to the master station a dedicated radio communication signal. The dedicated radio communication signal contains a type ID code associated with that signal, the ID code of the selected receiver, specific data associated with the selected receiver and the ID code of the transmitter. The selected receiver may be an aircraft or a slave ground station.
In a further aspect, the surveillance cycle starts with a first step in which the master ground station interrogates the selected aircraft with an interrogation signal S1. The selected aircraft responds to the interrogation signal with a first response signal S2 which includes the aircraft ID code and altitude and transmits that S2 signal to that master station. At the end of this step, the master ground station then determines the distance value to the selected aircraft by measuring the time delay between the moment of transmission of signal S1 and the moment of receiving the radio communication signal S2 from the selected aircraft and also is advised of the altitude of the aircraft via the response S2 signal from the aircraft. During these determinations of distance values, the determinations onboard the aircraft and at each ground station are assigned a fixed time period T1 for making such determinations, which time period is the same for all aircraft and ground stations. The time delay T1 is subtracted from the measured time delays in a given sequence.
In a next second step, the master ground station transmits a third signal to the same selected aircraft a different radio communication signal S3 containing the determined distance value between the master station and selected aircraft as measured on the ground. The selected aircraft receives the communication signal S3, and computes onboard the aircraft the distance value to the master ground station based on the time delay between the moments of transmitting to and receiving from master station of its radio communication signals, less the predetermined time period T1, and transmits to the master ground station a further radio communication signal S4 containing the distance value between the selected aircraft and master station, computed onboard that selected aircraft. At the end of the second step, all ground stations and all of the aircraft in that ATC airspace now know the distance value between the master station and selected aircraft, as measured on the ground since they all are in the range of the transmitted ground station and air and receive such signals. They all also receive the signals manifesting the same distance value measured onboard of the selected aircraft together with the altitude of selected the aircraft.
With this distance value, all slave stations then compute the distance value between the respective slave station and the selected aircraft by measuring the time delay between the moments of receiving the radio communication signals transmitted by master ground station and the selected aircraft, less the time period T1 which is the same for all aircraft. This measured time delay value is manifested by the unknown distance between the master station and selected aircraft, by the known distance between the master station and that slave station and by the unknown distance between the selected aircraft and that slave station. Immediately after the master station computes and transmits the distance value to the selected aircraft, each slave station then computes the remaining unknown distance value between the selected aircraft and that slave station.
At this moment in time, all ground stations now have the distance values to the selected aircraft, measured on ground, and the distance value between the selected aircraft and master station, measured onboard of selected aircraft. In the same time period, the selected aircraft has onboard the distance value to the master station, measured on ground and onboard that aircraft.
In a further aspect, to compute the 3D position of the selected aircraft, the ATC ground system needs the distance values to the selected aircraft from the master station and each of the slave stations. At the same time, the selected aircraft needs, for onboard 3D position calculations, the distance values to each slave ground station. To fulfill both needs, the master ground station interrogates, one by one, each slave station. When such interrogation radio communication signals are received, each slave station responds to the master station with a dedicated radio communication signal containing the ID code of selected aircraft and the distance value to selected aircraft, measured by that slave station. At the end of this process, all aircraft including the selected aircraft, and on the ground in the ATC system, know all of the distance values, measured on ground, between each ground station and selected aircraft.
In a further aspect, during the process of interrogation of slave ground stations, by the master station, the selected aircraft receives all of these transmitted radio signals from the master station and each slave station. Using the same procedure, the selected aircraft computes onboard the distance value to each slave station by measuring the time delay between the moments of receiving the interrogation signal transmitted by master station and responding signal transmitted by each slave station, less the time period T1, knowing the distance value to the master ground station.
In a further aspect, the selected aircraft has the distance values to each ground station, measured on the ground and onboard. Based on the determined distance values and known position of each of ground station, the selected aircraft computes onboard its 3D position. At the same time, the on ground ATC system computes the selected aircraft 3D position.
In a further aspect, during the interrogation process of all slave stations, by the master ground station, every aircraft in the ATC airspace includes means to employ the same procedure for measuring the time delay between the receiving moments of radio communication signals from the master station and each slave station. To compute the distance value between each aircraft and each slave station, each aircraft needs to know the distance value to the master ground station. To fulfill these needs, the master ground station includes means to transmit, at the end of the surveillance cycle, a dedicated radio communication signal containing a master station ID code and a UTC clock value, measured in milliseconds, microseconds, nanoseconds within the last UTC clock second, at the time of the start of the transmission of the later dedicated radio signal.
Thus a procedure is used by each aircraft and by the ground stations before the acceptance to the ATM database of the 3D aircraft determined position, wherein the onboard UTC clock being previously synchronized with the master ground station UTC clock, the distance value to the master ground station as computed onboard of each aircraft is based on the time delay values for the various signals between the ground stations and the aircraft until each aircraft receives the final dedicated radio communication signal from the master ground station.
Thus, also, at the moment in time of receipt of the final dedicated signal, all aircraft, in that ATC airspace, know precisely the 3D position of the selected aircraft and their own 3D position. At the same time, the UTC clock of all slave ground stations and selected aircraft are precisely synchronized with master station UTC clock, using the dedicated radio communication signal from the master station and having previously measured the distance value to the master station.
In a further aspect, the ground stations check and adjust, if needed, their respective precise oscillator frequency, used for distance measurements, by employing the difference between the known geographical distances between the ground stations and the same values measured by each ground station using their precise oscillator.
In a still further aspect, the selected aircraft use the same procedure as the ground stations to check and adjust its precise oscillator, used for distance measurements, by comparing the distance values to each ground station, as measured onboard and as measured at the ground stations. The distance values measured by the ground stations are used as the reference values to adjust the aircraft precise oscillator.
In a further aspect, the above procedure is repeated for each aircraft located in that ATC airspace based on their ID code provided by the ATM database. At the end of the surveillance process, an aircraft list is provided by ATM database, each aircraft in that ATC airspace passing through xe2x80x9cthe selected aircraftxe2x80x9d position status and, thus, all aircraft 3D positions are available, in the same time period, onboard each aircraft and on the ground at the ground stations corresponding to that ATC system location at that ATC system location.
Preferably, a complete surveillance process, including providing the 3D positions to all aircraft operating in one ATC airspace, is less than 10 seconds for an ACC area, and less than 4 seconds for an APP/TWR area.
Based on the above, the capacity of the ATC control system, in accordance with the present invention, to control and monitor the 3D position of any aircraft operating in one ATC airspace is believed to be practically unlimited and consequently believed to cover future traffic demands.
In a further aspect, a method of determining the 3D position of all active aircraft in a given ATC area comprises independently computing on board each aircraft the 3D position of all of aircraft in a given time period and selectively displaying the computed 3D positions.
In a further aspect, the independently computing step comprises transmitting signals between each said active aircraft and each of a plurality of ground stations, measuring the transmission time delay of certain of the signals and computing from the time delays the distances between each aircraft and said ground stations and between selected ground stations to each other.
In a further aspect, the ground stations comprise a master station and a plurality of slave stations, the transmission of signals including transmitting a first set of signals between the master station and a selected aircraft of the plurality of aircraft and then transmitting a second set of signals between the master station and each said slave station, a first set of said signals for use in said measuring step and a second set of said signals for transmitting the measured distances to and from the selected aircraft and the master station and a third set of signals for transmitting the measured distances to and from the master station and each said ground station to form a surveillance cycle.